A low-profile Substrate IntegratedWaveguide (SIW) cavity backed self-quadruplexing slot antenna supporting both microwave and mm-wave frequencies is proposed. Initially, a square SIW resonator is designed, and diagonally bisected into two half-mode resonators. A small portion of each section is assigned for mm-wave frequencies (28 and 30 GHz), and the remaining parts are adjusted to operate at microwave frequencies (4.8 GHz and 5.4 GHz). The microwave frequencies utilize the fundamental mode of the cavity and attain a maximum gain of 5.4 and 5.2 dBi at 4.8 and 5.4 GHz, respectively. The mm-wave resonators take advantage of higher order mode, resulting in a realized maximum gain of 8 and 8.7 dBi at 28 and 30 GHz. The simulated and measured results verified that at the mentioned frequencies, the reflection coefficients are below -20 dB, and the isolation among ports is better than 20 dB as well. Thus, it is asserted that the suggested antenna is a good candidate for 5G communication systems utilizing sub-6 GHz and mm-wave bands. This can be considered as the first self-quadruplexing antenna designed for both microwave and mm-wave frequencies.

A 1 $x$ 4 antenna feeding network is introduced with the capability of generating the required phase distribution for exciting orbital angular momentum (OAM) modes $\pm$ 1. The proposed structure includes an equal power divider and four 1-bit phase shifters. Switching the state of phase shifters between $\pm 45^\circ$ , [0, 90, 0, 90] phase distribution is achieved in clockwise and counterclockwise directions. In case a uniform circular array (UCA) with a mirror image configuration is used, the phase distribution of [0, 180, 180, 0] is automatically produced between the antenna elements. Thus, the combination of feeding network and UCA will bring about the desired condition for exciting OAM modes +1 and -1. Furthermore, it is explained that by cascading another phase shifter to each of existing ones, the possibility of generating OAM mode 0 is obtained. A prototype of the suggested structure operating at 2.45 GHz is designed, fabricated, and measured. Upon evaluating the radiation characteristics of the system, reconfigurable beams with helical phase fronts and owing the null in the broadside are observed.

Intelligent reflecting surfaces (IRS), also known as reconfigurable intelligent surfaces (RIS), have currently received much attention for their applications in wireless communication. The n-bit RISs presented in the literature are restricted to a single resonance and single polarization. These shortcomings create hurdles to engage more number of users and design a low-cost system (i.e., a separate hardware is required for each desired frequency band and each polarization). However, these issues can be solved if frequency reconfigurability and multiple polarization states (i.e., TE and TM) can be achieved in one structure. This paper presents a new multi-bit reconfigurable reflecting surface (RRS) with frequency-reconfigurable functionality working for both TE and TM polarized waves. The proposed design is tunable between 1.8-2.3 GHz and 2.95-3.9 GHz for TE and TM polarized electromagnetic (EM) waves, respectively. To simultaneously achieve the frequency reconfigurability and phase tailoring (varied from 0 ^$\circ$ to 315 ^$\circ$ ) in the proposed structure, the super-cell technique is used. This latter is incorporated in a phase gradient metasurface with different digital coding patterns to perform beam scanning and splitting functionalities. The simultaneous frequency reconfigurability and phase controlling for both TE and TM polarized waves, make this RRS a potential candidate for future RIS and reconfigurable devices.

In this paper, a wideband and high-gain circular polarised Fabry–Perot Resonator Antenna (FPRA) with a single partially reflective surface (PRS) layer is automatically generated and optimised using a VBA-based interface system between CST Microwave studio and Matlab. The proposed PRS layer is a promising superstrate for wideband and high-gain FP resonator antennas due to its relatively high reflection coefficient magnitude and positive phase gradient, which resemble that of the optimum PRS over the relevant frequency band. The circular polarisation was achieved using a sequential feeding network for a 2 × 2 array air-gapped slot-coupled elliptical patch antenna. The proposed design achieved an impedance bandwidth of 48.58% (15.3 GHz) ranging from 23.84 GHz to 39.14 GHz, and the −3 dB gain bandwidth was 22.42% (6.25 GHz) from 24.75 to 31 GHz, with a peak gain of 17.12 dB at 29 GHz, and an axial ratio bandwidth of 21.75% (6.2 GHz). In addition, the achieved radiation efficiency was 90%. Consistent and almost invariant radiation patterns are achieved over the millimetre-wave frequency band of interest. The experimental and simulated results are in good agreement, justifying the feasibility of the proposed design as a high-gain and wideband FP resonator array antenna for Mm-wave applications.

A compact self-quadruplexing antenna is presented, using substrate-integrated waveguide (SIW) technology and operating at 5.8, 7.4, 28, and 38 GHz. The design process is based on bisecting diagonally a square cavity into two triangles to obtain two HMSIW cavities. The right-upper corner of the structure is separated by slots to incorporate mm-wave frequencies. By utilizing five capacitive slots, independent frequency tuning in the operating frequency bands is achieved. To the best of our knowledge, this is the most compact quadruplexing antenna in the literature that operates at both mm-wave and microwave frequencies, and it has the best isolation between ports. The size of the antenna is 0.25 λg2 and the isolation between ports is less than -26 dB. A prototype of the antenna is fabricated and measured, showing a good agreement with the simulations, and therefore confirming the design approach.